1. Field of the Invention
The present invention relates to a high strength aluminum alloy whose metallic phase includes microcrystalline phases or amorphous phases mingling with microcrystalline phases.
2. Description of the Related Art
An amorphous alloy is defined as an alloy whose arrangement of the constituent atoms does not have the crystal-like long periodic regularity. In general, the amorphous alloy can be produced by rapidly quenching of a molten alloy, electrolyticaly depositing or sputtering. Regarding the physical properties, the amorphous alloy has been known that it has a wider variety of excellent physical properties than the corresponding crystalline alloy does.
In an Al alloy, it has been known well that the amorphous alloy can be obtained. For instance, as a metal-metal amorphous alloy, there has been an Al-Ln binary alloy in which "Ln" stands for Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho Er, Tm, Yb and Lu, or an Al-Ln-TM ternary alloy in which "TM" stands for V, Nb, Mo, Mn, Fe, Co and Ni.
In the Al-Ln binary alloy, the Vickers hardness (Hv) and the tensile strength (.sigma.f) enlarge as the content of the "Ln" increases. In the Al-Ln binary amorphous alloy, the maximum values of the Vickers hardness (Hv) and the tensile strength (.sigma.f) are 250 and 875 MPa, respectively. Further, in the Al-Ln-TM ternary amorphous alloy, a higher mechanical strength is available. For instance, in an Al-Ln-Ni ternary amorphous alloy, the maximum values of the Vickers hardness (Hv) and the tensile strength (.sigma.f) are 340 and 1,140 MPa, respectively. These maximum values exhibited by the Al-Ln-Ni ternary amorphous alloy remarkably exceed those exhibited by an Al crystalline alloy, e.g., 180 and 550 MPa. Thus, it is apparent that the Al amorphous alloys have excellent mechanical properties.
In Japanese Unexamined Patent Publication (KOKAI) No. 1-275,732, a composite substance is disclosed which includes amorphous phases or amorphous phases and microcrystalline phases and which has a tensile strength of from 87 to 103 kgf/mm.sup.2 (from 853.6 to 1,011 MPa ) and a yield strength of from 82 to 96 kgf/mm.sup.2 (from 804.6 to 941.9 MPa). The composite substance can be obtained by rapidly quenching and solidifying a ternary alloy expressed by a general formula, Al.sub.a M.sub.b X.sub.c, in which "M" stands for one or more metal elements selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Ti, Mo, W, Ca, Li, Mg, Si and Nb, "X" stands for one or more metal elements selected from the group consisting of Y, La, Ce, Sm, Nd, Hf, Ta and "Mm" (i.e., a misch metal), a content "a" falls in a range of from 50 to 95 atomic %, a content "b" falls in a range of 0.5 to 35 atomic %, and a content "c" falls in a range of 0.5 to 25 atomic %.
As earlier mentioned, in the Al-Ln-Ni ternary amorphous alloy, the superb mechanical strengths are available. Moreover, according to the 30th research paper by the 147th amorphous material committee of the Japan Society for the Promotion of Science, a research has been conducted on a quarternary alloy which includes Al.sub.88 Ni.sub.10 Y.sub.2 as the principal component and in which a part of the Ni elements are substituted by Mn, Fe, Co, Zr or the like. For instance, in an Al.sub.88 Ni.sub.5 Y.sub.2 Fe.sub.5 amorphous alloy, a higher tensile strength of 1,400 MPa can be obtained. In an Al.sub.88 Ni.sub.8 Y.sub.2 Mn.sub.2 amorphous alloy, a further higher tensile strength of 1,470 MPa can be obtained.
As having been described so far, the Al amorphous alloys or the alloys including the composite substance made of the amorphous phases and the microcrystalline phases have the tensile strength or the hardness which is twice that of the conventional Al crystalline alloy. The present inventors further investigated the specific gravity of the Al amorphous alloys and compared them with that of the other crystalline or amorphous alloys. The results of the investigation and comparison are summarized in Table 1 below.
TABLE 1 __________________________________________________________________________ Composition Specific Tensile Phase (in atomic %) Form Gravity Strength (MPa) __________________________________________________________________________ Crystalline Al--Zn--Mg--Cu Forged 2.8 550 Substance Crystalline Al--Si--Fe--Cu--Mg Extruded 2.9 700 Substance Amorphous Al.sub.88 Fe.sub.9 Mm.sub.3 Ribbon 3.3 870 Amorphous Al.sub.88 Ni.sub.8 Mn.sub.2 Y.sub.2 Ribbon 3.2 1,500 Amorphous Al.sub.88 Ni.sub.7 Fe.sub.3 Y.sub.2 Ribbon 3.2 1,410 __________________________________________________________________________
As can be readily appreciated from Table 1, the Al amorphous alloys have the large specific gravity. For instance, the Al.sub.88 Ni.sub.8 Mn.sub.2 Y.sub.2 alloy, i.e., the Al quarternary amorphous alloy, whose tensile strength is the highest has the specific gravity of 3.2, and the Al.sub.88 Fe.sub.9 Mm.sub.3 alloy has the specific gravity as large as 3.3. On the other hand, the conventional crystalline forged substance and the conventional extruded substance, i.e., the Al-Zn-Mg-Cu crystalline alloy and the Al-Si-Fe-Cu-Mg crystalline alloy, have the specific gravity as small as from 2.8 to 2.9, but they have the lower tensile strength, e.g., 700 MPa at the highest.
The reason for the large specific gravity of the conventional Al amorphous alloys is that they contained Fe, Ni, Mn or the like which have a larger specific gravity than Al does. Hence, it has been longed for an Al amorphous alloy which has a much lower specific gravity but which keeps the high tensile strength in order to reduce the weight of aircraft, automobiles or the like and improve the low-fuel consumption thereof.
The present invention has been developed in view of the aforementioned problem of the conventional Al amorphous alloys, i.e., the large specific gravity. It is therefore an object of the present invention to provide a novel Al amorphous alloy which has a much lower specific gravity than the conventional Al amorphous alloys do but which keeps the high tensile strength thereof.